Lunar modulation on the occurrence frequency of the afternoon counter-electrojet events at Trivandrum     

N.S. Sastri  B.R. Arora 《Planetary and Space Science》1981,29(10):1091-1094

Distribution, over the lunar age, of the frequency of occurrence of the afternoon counter-electrojet events at Trivandrum during the period 1959–1978 is examined in each of the calendar months. A strong lunar modulation on the occurrence frequency is seen in January; this may be related to the global enhancement of the lunar tide during January. The modulation is also prominent in April, although 62% of the events in that month occur irrespective of the lunar age. The occurrence frequency at Trivandrum appears to be least influenced by the Moon in the northern summer months.  相似文献   

Contributions from oceanic and ionospheric dynamos to the lunar daily variation at Alibag     

N. S. Sastri  B. R. Arora  D. R. K. Rao 《Geophysical Journal International》1979,59(1):155-160

Summary. The contributions from the oceanic and ionospheric dynamos, L_o and L_I respectively, to the geomagnetic lunar daily variation, L , at Alibag, a coastal station in the Indian equatorial region, are calculated from the L harmonics derived from a 41–yr long series of observations. The analysis in the calendar months shows a steady and significant ocean dynamo contribution in the vertical component, Z, in all the months except April. Examination, by an analysis of the data year by year, of the association of L_o and L_I with varying solar and magnetic activities reveals, surprisingly, a stable correlation between the magnetic activity index A _P and the oceanic part in the horizontal and vertical components but not in declination, which probably indicates the influence of induced currents, along the latitudes, on L _o.  相似文献   

Soft classification for sub-pixel land cover extraction     

R. S. Tiwari  Manoj K. Arora  T. Kailash 《Journal of the Indian Society of Remote Sensing》1999,27(4):225-234

With increasing resolution of the remotely sensed data the problems of images contaminated by mixed pixels arc frequent. Conventional classification techniques often produce erroneous results when applied to images dominated by mixed pixels. This may load to unrealistic representation of land cover, thereby, affecting efficient planning, management and monitoring of natural resources. Consequently, soft classification techniques providing sub-pixel land cover information may have to be utilised. From a range of soft classification techniques, the present study focuses on the utility of conventional maximum likelihood classifier and linear mixture modelling for sub-pixel. land cover classifications. The accuracy of the soft classifications has been assessed using distance measures and correlation co-efficient. The results show that linear mixture modelling has produced accuracies comparable to maximum likelihood classifier. Besides this the correlations between actual land cover proportions and proportions from linear mixture modelling, though not strong, arc statistically significant at 95% level of confidence. It has also been observed that the normalised likelihoods of maximum likelihood classifier also show strong correlations with the actual land cover proportions on ground and therefore has the potential to be used as a soft classification technique.  相似文献   

Reservoir induced seismicity in the Koyna–Warna region,India: Overview of the recent results and hypotheses     

V. O. Mikhailov  K. Arora  A. V. Ponomarev  D. Srinagesh  V. B. Smirnov  R. K. Chadha 《Izvestiya Physics of the Solid Earth》2017,53(4):518-529

The state of the art in the geological and geophysical study of the region of Koyna and Warna water reservoirs is reviewed. The probable geodynamical factors of induced seismicity are discussed. The detailed geophysical surveys, satellite geodetic data, and time history of the seismicity in the region reveal a complicated pattern of the structure and recent geodynamics of the region. The existing data suggest that the induced seismicity is here most likely to be caused by the regional (intraplate) stresses driving the displacements along the orthogonal network of the faults whose strength has dropped and continues decreasing due to the reservoir impoundment and operation processes. The evolution of the seismicity which started immediately after the rapid filling of the Koyna reservoir in the region of the dam, then rapidly expanded southwards and eventually became concentrated in the region of the subsequently constructed Warna reservoir shows that seismic events can be initiated by a number of factors whose contributions may vary with time. The key ones among them include reservoir loading and its seasonal variations; water saturation of the faults which guide the propagation of the front of fracture, increased permeability, and, probably, mineral transformations (hydrolysis) under the water level fluctuations in the reservoirs; and displacement of the front of the high pore pressure down to the main source zone of the earthquakes at a depth of 6–8 km. Based on the analysis presented in the paper, we outline the directions of the future research aimed at studying the nature and dynamics of induced seismicity in the region of large water reservoirs.  相似文献   

Microcracks in Basalt and Tonalite at Friction     

Vettegren  V. I.  Ponomarev  A. V.  Mamalimov  R. I.  Shcherbakov  I. P.  Arora  K.  Srinagesh  D.  Chadha  R. K. 《Izvestiya Physics of the Solid Earth》2019,55(6):879-885

Izvestiya, Physics of the Solid Earth - Abstract—The growth rate and size of microcracks formed in the surface layer of basalt and tonalite (granodiorite) at friction are studied using...  相似文献   

Electrical Conductance Map for the Kachchh Rift Basin: Constraint on Tectonic Evolution and Seismotectonic Implications     

P. B. V. Subba Rao  B. R. Arora  A. K. Singh 《Pure and Applied Geophysics》2014,171(9):2353-2370

Geomagnetic field variations recorded by an array of magnetometers spread across the Kachchh Rift basin are reduced to a set of induction arrows as a diagnostic of lateral electrical conductivity variations. A non-uniform thin-sheet electrical conductance model is developed to account for the salient induction patterns. It indicates that the imaged conductivity anomalies can be related to the sediment-filled structural lows in between the fault bounded uplifts. It is suggested that sagging structural lows preserved the marine sediments deposited during the Mesozoic sea transgression and later developed into first order embayment basins for the deposition of sediments in association with Late Eocene transgression. Depth integrated electrical conductance helped in mapping two depo-centres: along the ENE-WSW trending Banni half-Graben bounded by the Kachchh Main fault on the south and, second, along the Vinjan depression formed in response to the subsidence between the Vigodi fault and westward extension of the Katrol Hill fault together with the westward bending of the Median High. Presence of metamorphosed graphite schist clasts in shale dominated Mesozoic sequence and/or thin films of carbon resulting from the thermal influence of Deccan activity on Carbonate-rich formations can account for the high electrical conductivity anomalies seen in the depo-centres of thick Mesozoic and Tertiary sediments. Additionally two high conductivity zones are imaged encompassing a block defined by the 2001 Bhuj earthquake and its aftershocks. In agreement with gravity, magnetic and seismic velocity signatures, aqueous fluids released by recrystallizing magmatic bodies intruded in association with Deccan trap activity account for mapped high conductivity zones. High fluid pressure in such a fractured domain, surrounding the intruded magmatic plugs, perturb the regional stress concentrations to produce frequent and low magnitude aftershocks in the shallow section of the epicentral track of the 2001 Bhuj earthquake.  相似文献   

Distribution of clay-sized sediments in streambeds and influence of fine sediment clogging on hyporheic exchange     

Shivansh Shrivastava  Michael J. Stewardson  Meenakshi Arora 《水文研究》2020,34(26):5674-5685

In this work, the deposition of clay-sized fine particles (d₅₀ = 0.006 mm) and its subsequent influence on the dune-induced hyporheic exchange are investigated. Fine sand (D₅₀ = 0.28 mm), coarse sand (D₅₀ = 1.7 mm), and gravel (D₅₀ = 5.5 mm) grains were used to form homogenous model streambeds; one control - no clay input, and two treatments - increasing clay inputs for each grain type. The results indicate that the clogging profiles of clay-sized sediments may not be predicted accurately using the previously proposed metric based on the relative sizes of infiltrating and substrate sediments. Further, the depositional patterns vary with the initial concentration of clay particles in the surface water. The assessment of clogging profiles in coarse-grained model streambeds also reveals a preferential infiltration of the clay particles in the hyporheic downwelling regions. The results from the dye tracer test suggest that the accumulation of clay particles altered the exchange characteristics in the treatment flumes. For each grain size, the treatment flumes exhibit lower hyporheic flux and higher median residence times compared to their respective control flumes. The dye penetration depths were lower in treatment flumes with fine and coarse sand compared to their respective control flumes. Interestingly, higher penetration depths were observed in treatment flumes with gravel compared to their respective control flume potentially due to the generation of preferential flow paths in the partially clogged gravel beds. The clogging altered the hyporheic fluxes and residence times in the coarse-grained model beds to a greater degree in comparison to the fine sand beds. Overall, our findings indicate that the properties of both fine and substrate sediments influence the clogging patterns in streambeds, and the subsequent influence of fine sediment clogging on hyporheic exchange and associated processes may vary across stream ecosystems.  相似文献   

Study of isotopic seasonality to assess the water source of proglacial stream in Chhota Shigri Glaciated Basin,Western Himalaya     

Naveen Kumar  Alagappan Ramanathan  Aman Arora  Mohd Soheb  Arindan Mandal  Parmanand Sharma  Shyam Ranjan 《水文研究》2020,34(5):1285-1300

The impact of surface melt patterns and the Indian summer monsoon (ISM) is examined on the varying contributions of end member (snow, glacier ice, and rain) to proglacial streamflow during the ablation period (June–October) in the Chhota Shigri glaciated basin, Western Himalaya. Isotopic seasonality observed in the catchment precipitation was generally reflected in surface runoff (supraglacial melt and proglacial stream) and shows a shift in major water source during the melt season. Isotopically correlated (δ¹⁸O–δD) high deuterium intercept in the surface runoff suggests that westerly precipitation acts as the dominant source, augmenting the other snow- and ice-melt sources in the region. The endmember contributions to the proglacial stream were quantified using a three-component mixing. Overall, glacier ice melt is the major source of proglacial discharge. Snowmelt is the predominant source during the early ablation season (June) and the peak ISM period (August and September), whereas ice melt reaches a maximum in the peak melt period (July). The monthly contribution of rain is on the lower side and shows a steady rise and decline with onset and retreat of the monsoon. These results are persistent with the surface melt pattern observed in Chhota Shigri glacier, Upper Chandra basin. Moreover, the role of the ISM in Chhota Shigri glacier is unvarying to that observed in other glacierized catchments of Upper Ganga basin. Thus, this study augments the significant role of the ISM in glacier mass balance up to the boundary of the central-western Himalayan glaciated region.  相似文献   

Magnetometer array studies in India: Present status,data interpretation and assessment of numerical modelling results     

B. R. Arora 《Journal of Earth System Science》1990,99(4):693-716

Significant results from several array of magnetometers deployed in India to probe deep geoelectrical structures of the crust and the upper mantle are reviewed in this paper. Emphasis is on critical appraisal of earlier results so that the article summarizes what has been done so far and what caution is to be taken on future work. Two large-scale arrays over northwest and peninsular India during 1979–80, have been followed up with six more linear or two-dimensional arrays over different parts of the country. “Trans-Himalayan” conductor aligned along the strike of Aravalli range, delineated by arrays over northwest India, essentially represents one of the major continental induction anomalies mapped by electromagnetic methods. Efforts for quantifying the induction effects through numerical models are shown to be constrained due to the large inter-station spacing, lack of information on the regional background conductivity distribution and the non-inclusion of the frequency dependence of induction effects. A more comprehensive modelling, not biased by these factors, enables approximating the Trans-Himalayan conductor as an asymmetric domal upwarp in the middle and lower crust located between Delhi-Hardwar ridge and Moradabad fault. Numerical modelling results for southern peninsular, despite the constraints, indicate that the strong and complex induction pattern can be adequately attributed to the combination of conductors connected with triple junction between Indo-Ceylon Graben, Comorin ridge and the west coast rifting. Induction features derived from the Valsad array, operated over basalt-covered region of western India, demarcate an enhanced conducting zone beneath Plume-associated triple junction in the Gulf of Cambay, apart from characterizing the presently active seismic zone as a resistive block.  相似文献   

Seminal role of stratiform clouds in large-scale aggregation of tropical rain in boreal summer monsoon intraseasonal oscillations     

Kumar  Siddharth  Arora  Anika  Chattopadhyay  R.  Hazra  Anupam  Rao  Suryachandra A.  Goswami  B. N. 《Climate Dynamics》2017,48(3-4):999-1015

Climate Dynamics - Modification of the vertical structure of non-adiabatic heating by significant abundance of the stratiform rain in the tropics has been known to influence the large-scale...  相似文献